Crack Propagation Mechanism And Model Of A Nickel-base Powder Superalloy

In the aeroengine,the cast and wrought alloy can be replaced by a powder superalloy.Under actual aero engine service conditions,the operating temperature of the hot end component turbine disk rim is between 650 ? and 700 ?,which is a harsher service environment.Establishing accurate crack propagation models is one of the basic requirements for the damage tolerance design of powder disk.In this paper,assessment of the high temperature crack propagation of a new type of nickel-based powder superalloy was carried out.The effects of temperature,load ratio and load-holding time on the crack propagation behavior were studied.The crack growth rate model was constracted and evaluated.The main work and conclusions are as follows:(1)According to the actual size of the nickel-based powder alloy dual properties simulation disk,a reasonable crack propagation test specimen was designed,the test scheme was planned,the high temperature crack growth test was carried out,and the test results were discussed and analyzed.When the grain sizes are similar,the primary ?' has a greater influence on the crack propagation behavior.When the difference of grain size is large,the effect of grain size on the crack growth rate is large,and as the crack growth rate increases,the size effect is weakened.When the temperature is low,the 550°C propagation mode is transgranular,and the propagation rate is low.When T is greater than 600°C,the propagation mode is transgranular-intergranular.The higher the temperature,the larger the proportion of intergranular propagation,and the higher the crack growth rate.Comparison of the holding time shows that the holding time is shorter,the oxidation is weaker,mainly resulting in the transgranular propagation.There are a large number of fatigue striation,and the holding time increases and the proportion of intergranular increases.(2)The crack propagation data was described using hyperbolic sinusoidal model,Paris model and Forman model,respectively,and the models were evaluated.The hyperbolic sinusoidal model,Forman model,and Paris model have good characterization capabilities for high temperature fatigue crack propagation.The interpolated and extrapolated model predictions of the temperature T and the stress ratio R are performed by using the interpolated hyperbolic sinusoidal model.The results show that the crack propagation rate curve of the interpolated hyperbolic sinusoidal model has high precision when propagation mechanism is the same.As crack propagation mode changes,the interpolated hyperbolic model describes the fatigue propagation data poorly.The evaluation results of the three models show that the Paris model has high characterization ability of high temperature fatigue crack growth life,and the prediction results are all within 2 times scatter band;the Forman model is the worst.Compared with the double Paris model,the hyperbolic sinusoid model has better ability to describe high temperature creep crack propagation and has less scatter.The high temperature creep-fatigue crack growth rate obtained by the direct superposition model is much larger than the experimental value.The modified Saxena model reduces the time-dependent crack growth rate weight,which is consistent with the high temperature creep-fatigue test data.(3)According to the "tunneling effect" of crack propagation in the experiment,the literature survey was carried out,and the CT specimen with side groove was optimized.Comparative test were carried out.The optimal side groove shape is a V-shaped side groove characterized by 3 parameters.Tests have shown that optimizing the shape of the side groove can effectively reduce the variation of the crack length along the thickness direction.